While the present invention can be applied to, for instance, any Ellipsometer or Polarimeter and the like System, Spectroscopic Ellipsometers (SE's) will be utilized as a primary, and very relevant, example herein.
Spectroscopic ellipsometer (SE) systems for use in the investigation and characterization of physical and optical properties of Sample Systems over a large range of wavelengths, are well known. Briefly, such (SE) systems operate by monitoring changes effected in the polarization state of a beam of light when said beam of light is caused to interact with a sample system (SS).
Spectroscopic ellipsometer (SE) systems typically comprise a Polarization State Generator, and a Polarization State Detector. In use, the polarization State Generator causes a beam of light in an intended state of polarization to be incident upon a Sample System (SS) at a set Angle of Incidence (AOI), and the Polarization State Detector monitors a reflected and/or transmitted beam of light which emerges from said Sample System (SS) and at least partially determines the polarization state thereof. (Note that a completely defined "Polarization State" of a polarized Light Beam requires designation of intensity ratio and retardation phase angle between quadrature components thereof, as well as an absolute reference intensity, and the "Handedness", (direction of rotation), thereof. Typical Rotating Element Ellipsometers (REE's) determine only a partial polarization state consisting of an intensity ratio and phase angle.)
Continuing, Spectroscopic Ellipsometer (SE) systems fall into general categories such as:
a. Rotatable Element Nulling Ellipsometers (RENE); PA1 b. Rotatable Element Automated Nulling Ellipsometers (REANE)); PA1 c. Phase Modulation Ellipsometers (PME); PA1 d. Rotating Analyzer Ellipsometers (RAE); PA1 e. Rotating Polarizer Ellipsometers (RPE); PA1 f. Rotating Compensator Ellipsometers (RCE); PA1 g. Rotating Polarizer and Analyzer Ellipsometers (RPAE); PA1 h. Rotating Polarizer and Analyzer, Fixed Compensator Ellipsometers (RPAFCE); PA1 i. Rotating Analyzer and Compensator, Fixed Polarizer Ellipsometers (RACFPE); PA1 j. Rotating Polarizer and Compensator, Fixed Analyzer Ellipsometers (RPCFAE); PA1 k. Rotating Analyzer, Fixed Polarizer and Compensator Ellipsometers (RAFPCE); PA1 l. Rotating Polarizer, Fixed Analyzer and Compensator Ellipsometers (RPFACE); PA1 m. Rotating Compensator, Fixed Analyzer and Polarizer Ellipsometers (RCFAPE); PA1 n. Rotating Analyzer and Compensator, Fixed and Polarizer (RACFPE). PA1 a. a source of a beam of light; PA1 b. a means for imposing an intended state of polarization thereto; PA1 c. a detector system for use in developing a signal from said beam of light after it interacts with said Sample System, which signal contains information that allows determination of optical and physical properties of said Sample System, and PA1 d. a means for analyzing said developed signal after it interacts with a Sample System. PA1 a. a source of a beam of light, the wavelength of which beam of light can be determined by a user; PA1 b. a Polarizer (P) for use in setting a polarization state in said beam of light provided by said source of a beam of light. PA1 a. a Rotating Analyzer (RA), for use in processing said polarized beam of light after it interacts with a Sample System (SS), that a linearly polarized beam of light of varying intensity is produced; and PA1 b. a Detector System (DET) for use in developing a signal from said beam of light after it emerges from said Rotating Analyzer (RA), which signal contains information which allows determination of the optical and physical properties of said Sample System. PA1 a. providing a beam of light of an intended wavelength from said source of a beam of light; PA1 b. orienting said beam of light so that it approaches a present Sample System (SS), optical and/or physical properties of which are to be determined, at an Angle Of Incidence (AOI) near the "Principal" or "Brewster" angle for said Sample System (SS); PA1 c. setting the Polarizer (P) to a known fixed position, so that its Azimuth is oriented so as to impose a desired state of polarization upon said beam of light; PA1 d. causing said beam of light, after interaction with said Sample System (SS) to pass through said Rotating Analyzer (RA) and emerge therefrom as a modulated, typically varying intensity with time, beam of light; and PA1 e. causing said typically time varying intensity beam of light to enter a Detector System (DET), which Detector System (DET) produces a signal, the analysis of which allows determination of the optical and/or physical properties of the Sample System (SS). PA1 a. a source of a beam of light, the wavelength of which beam of light can be set as desired by a user; and PA1 b. a Polarizer (P) for use in setting a polarization state in said beam of light provided by said source of a beam of light. PA1 a. a Rotating Analyzer (RA), for use in processing said polarized beam of light after it interacts with a Sample System (SS), so that a linearly polarized beam of light of typically varying intensity is produced; and PA1 b. a Detector System (DET) for use in developing a signal from said beam of light, after it emerges from said Rotating Analyzer (RA), which signal contains information which allows determination of optical and physical properties of said Sample System (SS). PA1 a. a polarization state generator system comprising: PA1 b. a polarized beam modulation element; PA1 c. a sample system; and PA1 d. a polarization state detector system comprising: PA1 a. a system of at least two fixed-order-waveplate-type retarders which can be rotated with respect to one another, each about an axis perpendicular to an optical axes thereof, said optical axes being parallel to the surface of said fixed-order-waveplate-type retarders; PA1 b. a Babinet dual wedge-type variable retarder; PA1 c. a Soleil dual wedge-type variable retarder; PA1 d. a Kerr electro-optical-type variable retarder; PA1 e. a Pockels electro-optical-type variable retarder; PA1 f. a liquid crystal electro-optical-type variable retarder; PA1 g. a Voigt magnetic-faraday-effect variable retarder; and PA1 h. a Cotton-Mouton magnetic-faraday-effect variable retarder. PA1 a. a stationary polarizer; PA1 b. a stationary analyzer; PA1 c. a stationary compensator; PA1 d. a rotating polarizer; and PA1 e. a rotating analyzer. PA1 a. measuring a plurality of sample system ellipsometric first and ellipsometric second parameter pairs, as a function of at least one means for setting a polarization state in said beam of light setting(s), and a plurality of variable retarder settings; and PA1 b. applying a mathematical technique to said plurality of measured ellipsometric first and ellipsometric second parameter pairs to determine PSI and DELTA values for said sample system per se. while compensating for the presence of said variable retarder. PA1 a. measuring a plurality of sample system ellipsometric first and ellipsometric second parameter pairs corresponding to, at each of at least one means for setting a polarization state in said beam of light setting(s), at least five Berek-type retarder settings, said Berek-type retarder settings including no-tilt, clockwise and counterclockwise elevational, and clockwise and counterclockwise azimuthal tilts; and PA1 b. applying a mathematical technique to said plurality of measured ellipsometric first and ellipsometric second parameter pairs to determine sample system PSI and DELTA values, while compensating for presence of said at least one Berek-type variable retarder. PA1 a. measuring a plurality of sample system ellipsometric first and ellipsometric second parameter pairs as a function of at least one means for setting a polarization state in said beam of light setting(s), and a plurality of variable retarder settings; and PA1 b. applying a mathematical technique to said plurality of measured ellipsometric first and ellipsometric second parameter pairs to determine sample system PSI and DELTA values, while compensating for the presence of said at least one variable retarder. PA1 a. a system of at least two fixed-order-waveplate-type retarders which can be rotated with respect to one another, each about an axis perpendicular to an optical axes thereof, said optical axes being parallel to the surface of said fixed-order-waveplate-type retarders; PA1 b. a Babinet dual wedge-type variable retarder; PA1 c. a Soleil dual wedge-type variable retarder; PA1 d. a Kerr electro-optical-type variable retarder; PA1 e. a Pockels electro-optical-type variable retarder; PA1 f. a liquid crystal electro-optical-type variable retarder; PA1 g. a Voigt magnetic-faraday-effect variable retarder; and PA1 h. a Cotton-Mouton magnetic-faraday-effect variable retarder. PA1 a. providing a modulation element ellipsometer (MEE) system which enables accurate and precise determination of PSI and DELTA values of essentially any investigatable sample system; PA1 said modulation element ellipsometer (MEE) system comprising means for setting at least one polarization state in a beam of polarized light and means for identifying, and means for monitoring, a polarization state in said polarized beam of light, after an interaction thereof with a sample system; PA1 between said means for setting at least one polarization state in a beam of polarized light and said means for monitoring a polarization state in said polarized beam of light, there being present at least one adjustable means for controlling an ellipsometric phase angle between orthogonal components in a polarized beam of light, which adjustable means for controlling an ellipsometric phase angle, in use, allows sequentially setting a plurality of ellipsometric phase angles between orthogonal components in a polarized beam of light which is caused by said ellipsometer system to interact with a sample system, such that in use said ellipsometric phase angle can be set sequentially through a plurality of settings while ellipsometric data is obtained by said means for monitoring a polarization state in said polarized beam of light at at least two selected settings of said at least one adjustable means for controlling an ellipsometric phase angle; which obtained ellipsometric data can be utilized in determination of PSI and DELTA values of an investigated sample system, where said determination of said PSI and DELTA values includes compensating for the effects on said obtained ellipsometric data of said at least two selected setting of said at least one adjustable means for controlling an ellipsometric phase angle, on said obtained ellipsometic data; PA1 said modulation element ellipsometer (MEE) system being further comprised of computational means which performs determination of investigated sample system PSI and DELTA values, which computational means utilizes data obtained with said at least one adjustable means for controlling ellipsometric phase angle between orthogonal components in a polarized beam of light, being set to at least two selected settings, and which computational means performs compensation of the effects of said at least one adjustable means for controlling ellipsometric phase angle between orthogonal components, on said utilized ellipsometric data obtained at said at least two selected settings of said at least one adjustable means for controlling ellipsometric phase angle between orthogonal components, in determining sample system PSI and DELTA values; PA1 b. placing a sample system to be investigated into said modulation element (MEE) ellipsometer system and causing a beam of polarized light from said means for setting at least one polarization state in a beam of polarized light to interact therewith and enter said means for monitoring a polarization state; PA1 c. adjusting said at least one adjustable means for controlling ellipsometric phase angle between said orthogonal components to be sequentially set to a plurality of settings while ellipsometric data is obtained by said means for monitoring a polarization state in said polarized beam of light at at least two selected settings from said plurality settings of said at least one adjustable means for controlling a value of ellipsometric phase angle between said orthogonal components; PA1 d. causing said computational means to determine investigated sample system PSI and DELTA values by a method which performs compensation of the effects of said at least one adjustable means for controlling ellipsometric phase angle between orthogonal components in a polarized beam of light on said ellipsometric data obtained at said at least two selected settings of said at least one adjustable means for controlling ellipsometric phase angle between orthologonal components in a polarized beam of light which is caused to interact with a sample system, in determining sample system PSI and DELTA values; and PA1 e. optionally determining at least some of members of the group consisting of: (the "Handedness", Stores Vector, and Jones and Mueller Matrix components) of said polarized beam of light and investigated sample system.
(Note that similar definitive descriptions also apply to Polarimeter and the life Systems).
The above, non-exhaustive, catagorization is based upon what system components are present and how said system components are used. It is noted that a review Article by Collins, Rev. Sci. Instrum. 61 (8), August 1990 provides a discussion of various ellipsometer configurations.
Generally, all Ellipsometer Systems include elements comprising:
While the present invention is applicable to essentially all types of Ellipsometer or Polarimeter and the like systems which contain Rotatable, Rotating, and/or Modulation elements, the present Disclosure will use, as a non-limiting example, a J.A. Woollam Co. Inc. Variable Angle Spectroscopic Ellipsometer (VASE--Registered Trademark), (RAE) system. It is emphasized, however, that the general principals involved in the present invention are generally applicable to any Ellipsometer or Polarimeter and the like system which contains rotatable, rotating and/or modulation elements, examples of which were listed infra.
In more detail then, a Spectroscopic Rotating Analyzer Ellipsometer (RAE) system comprises
1. A Polarization State Generator (PSG) System, comprising:
2. A Polarization State Detector (PSD) System, comprising:
A typical procedure utilizing a conventional (RAE) system to determine the optical and/or physical properties of a Sample System (SS) involves the steps of:
While not a focus of the present invention, previous work by the J.A. Woollam Co. Inc. has determined that it is preferable to apply a non-linearly, (eg. elliptically and preferably essentially circularly polarized), beam of light to a Detector Element (DE). This is because typical Detector Elements demonstrate undesirable Polarization Dependent Sensitivity characteristics. That is, typical Detector Elements respond differently to equal intensity polarized light beam in states of polarization, (eg. the elliptical or linear orientation of a beam), and thereby introduce Detector Element caused errors to resulting determined values which do not represent optical and/or physical Sample System properties per se. Said Detector Element operational inconsistency is, however, in typical Detector Elements, minimized when an essentially circularly polarized or even a non-polarized beam of light is applied thereto, rather than linearly polarized beam of light, such as that which emerges from a Rotating Analyzer (RA). It is noted that linearly polarized light is converted to elliptically polarized light by passage through a Birefringent Retarder which serves to adjust the phase angle between well known "P" and "S" components in a polarized beam of light. (Note, "P" refers to that component of a polarized beam of light in a plane containing the normal to a Sample System and the incident and reflected or transmitted beams, while "S" refers to that component perpendicular thereto, and parallel to the surface of said sample system. Also, it is noted that past a Rotating Analyzer (RA), the relevance of "P" and "S" components is generally lost and it in typical practice Light Beam components are then defined by a coordinate system imposed with respect to a Detector Element rather than a Sample System).
Continuing, it is to be understood that the Rotating Analyzer Ellipsometer example (RAE) system described above, typically is best applied when a beam of polarized light is oriented so that it impinges upon a Sample System (SS) at the "Principal" or "Brewster" Angle Of Incidence (AOI), (note that the terms "Principal" and "Brewster" are used interchangably in this Disclosure), where the measured ellipsometer ellipsometric BETA parameter is essentially zero (0.0) and Sample System characterizing DELTA values are ideally near ninety (90) degrees. (Note that Principal and Brewster Angles refer to a condition whereat DELTA becomes ninety (90) degrees and note that BETA, and ALPHA, are Sample System characterizing values from which PSI and DELTA can be determined by direct application of a transfer function, or by indirect mathematical regression applied to a multiplicity of measured ALPHA-BETA pairs). If the (AOI) is set away from the Brewster Angle, (which for semiconductors is approximately seventy-five (75) degrees), the quality, (eg. usable accuracy and precision), of data obtainable from a (RAE) as indicated infra is degraded. The requirement for operation at the Brewster Angle thus sets a serious limitation on the utilizations of (RAE's). Prior work by the J.A. Woollam Co. Inc. has determined that data obtained from a (RAE) in which the (AOI) is set in excess of the Brewster Angle, can, in some circumstances be of a sufficient quality to allow use in measuring Sample System PSI and DELTA values. Such is the topic in Copending patent application Ser. No. 08/327,107 from which this Application is a CIP. However, the further away an (AOI) is from the Brewster Angle, the more difficult it is to obtain usably precise and accurate data, and any data acquired has associated therwith a greater uncertainty as regards its accuracy, (ie. confidence the data is accurate is lower, and associated possible error greater). It should also be appreciated that the Brewster Angle depends on wavelength such that the ideal Angle Of Incidence (AOI) for one wavelength is not necessarily ideal at another. As a result, when a relatively large range of polarized light beam wavelengths is utilized it is typically necessary to adjust the Angle Of Incidence (AOI) to maintain a Brewster Angle over said relatively large range. It would be very convenient if this (AOI) did not have to be so adjusted as utilized polarized light beam wavelengths are changed. (Note it is to be understood that operation of an Ellipsometer System set to effect a Brewster Angle (AOI) between a polarized Beam of Light and a specific Sample System effects a DELTA of ninety (90) degrees and accompanying circular polarization in the reflected polarized Beam of Light. This is always optimum in that data obtained is accurate to within tighter limits than is possible if data is obtained with other than said polarized Light Beam-Sample System associated Brewster Angle. The present invention does not modify that basic relationship. What the present invention does do, however, is enable better Sample System PSI and DELTA data to be obtained using other than a Brewster Angle, because PSI and DELTA transfer function, (ie. a function which provides PSI and/or DELTA given ALPHA and/or BETA), sensitivity to noise and measurement errors in ALPHA and/or BETA is reduced by setting ALPHA and/or BETA values in ranges where said transfer function is less sensitive to said noise and measurement errors in ALPHA and/or BETA.)
It would be also be of benefit if any (AOI) could be utilized in an Ellipsometer System without unnecessarily limiting the Spectroscopic capability thereof. For instance, the J.A. Woollam VASE (RAE) system operates over a range of at least one-hundred-ninety (190) to seventeen-hundred (1700) nanometers, but because of physical constraints imposed by real-time-in-situ Sample System Processing Systems to which the (VASE).TM. is applied, it is not always convenient, or even physically possible, to set an appropriate Brewster (AOI) for a particular polarized light beam wavelength within said range. Restriction on possible (AOI's) then enter undesirable restrictions as to what polarized light beam wavelengths can be utilized and still allow the obtaining of data of a usable accuracy and precision to allow accurate determination of Sample System characterizing PSI and DELTA values therefrom. Again, it would be of benefit if any (AOI) could be used with essentially any polarized light beam wavelength without decreasing the capability to acquire sufficiently usably accurate and precise Sample System PSI and DELTA determining data.
As well, it is noted that typical Ellipsometers, such a described infra, are incapable of determining components of, for instance, a Jones or Mueller Matrix for a Sample System. (Ellipsometry, Polarimetry, Jones and Mueller Matricies, as well as Stokes Vectors and aspects of polarized light and utilization thereof etc., are described in references such as the text titled "ELLIPSOMETRY AND POLARIZED LIGHT", by Azzam and Bashara, North-Holland, 1977, which reference is incorporated by reference into this Disclosure). To obtain up to fifteen (15) of sixteen (16) Mueller Matrix elements, (with the sixteenth being a absolute reference value to which the other fifteen (15) are referenced in a ratio relationship), it is required that one or more Retarders be placed between the Polarizer (P) and Rotating Analyzer (RA) in Rotating Analyzer Ellipsometer (RAE) system, for instance. However, said Retarder(s) have effects on the polarization state of a polarized beam of light, which effect is not always desired. (It is noted that similar use of Retarders is applicable in any type Ellipsometer system). In known Ellipsometer Systems with such Retarder (s) present, undesired effects of said presence, including introduction of artifacts, can not be conveniently minimized. In particular, said Retarders introduce changes in the polarized beam polarization state, which changes are dependent upon wavelength, which dependence limits useful spectroscopic range. In known Ellipsometer Systems said Retarder(s) must be removed therefrom if the effects thereof are to be avoided. The ability to conveniently make one or more Retarders within an Ellipsometer System, end user "Transparent", over a large range of polarized light beam wavelengths, without removal thereof, would alone provide utility in the form of user convenience. That is, no known Ellipsometer System provides such Retarders in a manner such that they can conveniently be made to be essentially end-user "Transparent" by simple user adjustment, as opposed to removal thereof from said Ellipsometer System, over a large range of wavelengths and polarized beam of light (AOI's), emphasis added.
In addition, it is noted that it is difficult to determine the "Handedness", (eg. direction of rotation), of the polarization of a polarized beam of light used in a typical (REE). It would be of benefit to be able to conveniently identify "Handedness" as a natural consequence of the presence of present invention enabling additional components.
Continuing, it is known in the practice of ellipsometry, to adjust the Azimuth Angle (POL) of a Polarizer (P) in a (RAE), (or the Analyzer in an (RPE)), system for instance, to adjust the value of a measured ellipsometric ALPHA to be within a range in which the sensitivity of a PSI Transfer function, (which is known to be a function of said ellipsometric ALPHA), to noise and errors in measurement etc. in measured ellipsometric ALPHA are made essentially negligible. (Note, ALPHA relates to a Magnitude ratio of polarized light beam Quardrature Components in (REE's)). It has not however, to the Inventor's knowledge, been possible to perform a related procedure to adjust ellipsometric BETA to optimum values over a relatively large spectral range of wavelengths, (eg. one-hundred-ninety (190) to seventeen-hundred (1700) nanometers or greater), without introducing unwanted, difficult to compensate artifacts onto a polarized beam of light, without the inconvenient necessity to change elements in said (REE). (Note, BETA relates to a retardation phase angle present between polarized light beam quadrature components in (REE's)).
For instance, using an (RAE) as an example, it would be of great utility were it possible to adjust the measured value if ellipsometric BETA to be within a range in which the sensitivity of a DELTA determining transfer function, (which is known to be a function of ellipsometric ALPHA and ellipsometric BETA), to noise and measurement errors etc. in measured ellipsometric ALPHA and ellipsometric BETA, is made essentially negligible. It would be especially convenient if such could be achieved by placing Varaible Retarder(s) between a Polarizer (P) and an Analyzer (A) in a (REE), such as required to allow obtaining Jones or Mueller Matrix components, which Retarder(s) would allow setting a measured ellipsometric BETA value within a range in which DELTA Transfer function sensitivity to noise and errors in measurement etc. of ellipsometric BETA are made essentially negligible, emphasis added. (It is noted that where ellipsometric ALPHA and ellipsometric BETA are each near zero (0.0) the modulation amplitude of detected intensity in an (REE) system is minimal).
In view of the above, it can be concluded that a system and method of its use which would allow usably accurate and precise data to be achieved from an Ellipsometer or Polarimeter and the like System of any type over a large, continuously variable range of wavelengths and/or (AOI's); and which would allow setting a Polarization State in a Polarized Light Beam, (or alternatively stated, simulating a "Composite Sample System" which presents with a PSI and DELTA in ranges in which they can be accurately measured), such that measured Amplitude Ratio and retardation Phase Angle between Polarized Light Beam Quadrature Components are set in ranges wherein the sensitivity of PSI and DELTA transfer function to noise and measurement errors etc. in, for instance, measured ALPHA and BETA values, are made essentially negligible, would be of great utility. It would be of further utility if said system and method of its use could, as a natural consequence of the presence and utilization thereof respectively, be adapted to allow determination of Jones or Mueller Matrix components. It would also be of utility if an Ellipsometer or Polarimeter and the like system, adapted with present invention system could, by simple user adjustment, be oriented so that added elements were made essentially end user transparent, thereby allowing use of an adapted Ellipsometer or Polarimeter and the like System in an essentially unadapted mode, without requiring that any elements be removed therefrom. It is emphasized that it would especially be of utility if said adapted Ellipsometer or Polarimeter and the like System could be conveniently utilized over a relatively large range of wavelengths without the necessity of System Component replacement.
A Search for relevant Patents which describe systems and/or methods which might be capable of providing the identified utility produced very little. In view of the fact that the present invention system, as is described supra in this Disclosure, in the Disclosure and Detailed description Sections, comprises Variable Retarder(s) (VR's) placed between a Polarizer and Analyzer in a Spectroscopic Rotating Element Ellipsometer, which Variable Retarders (VR's) are effective over relatively large spectral and Angle of Incidence ranges, the Search was focused upon systems which might be interpreted to provide said elements at said locations, or the equivalent effects thereof. Identified Patents are U.S. Pat. No. 3,741,661 to Yamamoto et al.; U.S. Pat. No. 4,176,951 to Robert et al.; U.S. Pat. No. 5,181,080 to Fanton et al.; U.S. Pat. No. 5,311,285 to Oshige; U.S. Pat. No. 5,335,066 to Yamada et al. Also U.S. Pat. No. 4,053,232 to Dill et al; and U.S. Pat. No. 5,329,357 to Bernoux et al. were identified. None of said Patents are considered to be particularly relevant. Patents which describe ellipsometers to which the present invention can be applied are, for instance, U.S. Pat. No. 5,373,359 to Woollam et al., and U.S. Pat. No. 5,416,588 to Ducharme et al., which Patents apply to Rotating Analyzer and Modulator Ellipsometers respectively, were also identified. Another identified Patent, to Dill et al., U.S. Pat. No. 3,880,524, describes the use of a quarter-waveplate Compensator between a Polarizer and a Rotating Analyzer in a Rotating Analyzer Ellipsometer (RAE), such that the state of pollarization of a reflected beam of light from a Sample System can be varied arbitrarily by merely adjusting the angular position (azimuths) of the Polarizer and said quarter-waveplate Compensator. Said quarter-waveplate compensator an be placed ahead or after a Sample System. The system described in Dill et al. provides a means for adjusting both ellipsometric ALPHA and ellipsometric BETA in a polarized beam of light, which polarized beam is "monochromatic". No teachings as how to conveniently make said system applicable over a relatively large spectroscopic range of wavelengths, however, is present. It is emphasized that the Dill et al. 524 Patent is to a monochromatic system, with no convenient provision for expanding to a relatively large spectral range without system element replacement, (that is, a different quarter-wave-plate would be required at each wavelength utilized, and a user would have to disassemble the Dill et al. ellipsometer system and replace such each time a different wavelength was used). The above referenced book by Azzam and Bashara briefly mentions the use of a Variable Retarder, (Babinet-Soleil type), to control relative retardation of Quadrature Components in a polarized Light Beam in Nulling Ellipsometers, but discourages such use because of associated poor resolution capability, (see page 166, footnote 9). Additionally, no teachings were found as how to make added system elements essentially end-user "transparent" at a desired wavelength, cover a large range of wavelengths, without removal thereof from said Ellipsometer System. This is a very important point. Also disclosed is an Article by Johs, titled "Regression Calibration Method For Rotating Element Ellipsometers, Thin Solid Films, 234 (1993). This article describes a regressions approach to calibration of rotating element ellipsometers, and is relevant to the present invention, as the present invention, in part, utilizes a mathematical regression procedure to indirect evaluation of PSI and DELTA Sample System Charaterizing parameters, and is incorporated herein by reference. Another article, which is also incorporated herein by reference, titled "Data Analysis for Spectroscopic Ellipsometry ", by Jellison Jr., Thin Solid Films, 234, ( 1933) p. 416-422, is identifed as it describes a method of determining the accuracy with which certain data points, (for instance, ALPHA or BETA values), can be measured, which information allows adding a weighting factor to a curve fitting regression procedure as applied to a multiplicity of said data, which weighting factor serves to emphasise the effect of more accurate and precise data.
While prior art describes the use of Variable Retarders in Ellipsometer or Polarimeter and the like Systems, none known to, the Inventors describes the application of relatively low Polarization State Artifact introducing Variable Retarder(s) to allow user adjustment of the Polarization State of an investigatory polarized beam of light in an Ellipsometer or Polarimeter and the like System, such that a "Composite Sample System" comprised of a seriesed combination of said relatively low Artifact introducing Variable Retarder and a Sample System per se. can be investigated over a full range of Sample System characterizing PSI and DELTA values, (including Sample Systems with PSI and DELTA values in ranges wherein said Ellipsometer or Polarimeter and the like System normally has difficulty in making measurements, (eg. DELTA's near zero (0.0) and one-hundred-eighty (180) degrees in Rotating Analyzer, Rotating Polarizer and Modulation Ellipsometers). In addition, no prior art obviates the capability of relatively low Polarization State Artifact introducing Variable Retardre(s) to enable Ellipsometer or Polarimeter and the like Systems to be operated over a large range if polarized light beam wavelengths, (eg. one-hundred-ninety (190) to seventeen-hundred (1700) nanometers), with only user adjustment of Variable Retarder(s) being required, rather than replacement thereof, nor does any prior art obviate the capability of low Polarization Variable Artifact introducing Variable Retarder(s) to enable Ellipsometer or Polarimeter and the like Systems to provide usably accurate and precise data when polarized light beams therein are oriented at other than a Principal or Brewster angle with respect thereto.
There is then demonstrated a need for a convenient to use system and method for improving data acquisition capability of spectroscopic ellipsometer and polarimeter and the like systems.
The present invention meets the identified need.